Low pressure generator for gas turbine engine

ABSTRACT

A gas turbine engine and methods of operation include a low pressure electric motor-generator arranged for selective operation in a generator mode to generate electrical power or a drive mode to assist rotation of a low pressure drive shaft of the engine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application Nos. 62/338,201, filed 18 May 2016; 62/338,204, filed18 May 2016; 62/338,205, filed 18 May 2016; and 62/433,576, filed 13Dec. 2016, the disclosures of which are now expressly incorporatedherein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to gas turbine engines, andmore specifically to auxiliary electric power generators of gas turbineengines.

BACKGROUND

Gas turbine engines are used to power aircraft, watercraft, electricalgenerators, and the like. Gas turbine engines typically include acompressor, a combustor, and a turbine. The compressor compresses airdrawn into the engine and delivers high pressure air to the combustor.In the combustor, fuel is mixed with the high pressure air and isignited. Exhaust products of the combustion reaction in the combustorare directed into the turbine where work is extracted to drive thecompressor and, sometimes, an output shaft, fan, or propeller. Portionsof the work extracted from the turbine can be used to drive varioussubsystems such as generators.

SUMMARY

The present disclosure may comprise one or more of the followingfeatures and combinations thereof. According to an aspect of the presentdisclosure, a turbofan gas turbine engine for use in an aircraft mayinclude a low pressure spool including a fan rotor arranged at a forwardend of the engine, a low pressure turbine rotor arranged at an aft endof the engine, a low pressure drive shaft extending along an axis androtationally coupling the fan rotor to receive driven rotation from thelow pressure turbine rotor, a high pressure spool including a compressorrotor, a high pressure turbine rotor, and a high pressure drive shaftextending along the axis and rotationally coupling the compressor rotorto receive driven rotation from the high pressure turbine rotor, and anelectric generator including generator core having a stator arrangedabout the low pressure drive shaft and a generator rotor rotationallycoupled to the low pressure drive shaft, the electric generator beingpositioned axially between the fan rotor and the compressor rotor alongthe axis.

In some embodiments, the low pressure drive shaft may include a fanshaft and a quill shaft having a base rotationally coupled with the fanshaft and a flange extending radially from the base for rotationalconnection with the generator rotor of the electric generator.

In some embodiments, the base of the quill shaft forms a quillconnection with the fan shaft that may be rotationally fixed but mayallow relative movement between the quill shaft, and wherein thegenerator rotor is mounted to a rotor hub forms another quill connectionwith the quill shaft.

In some embodiments, the base of the quill shaft may include a number ofsplines extending radially inward for connection with a number ofsplines of the fan shaft to rotationally couple the quill shaft and thefan shaft.

In some embodiments, the fan shaft may include a first bearing and asecond bearing each arranged to support the fan shaft for rotation aboutthe axis, and the electric generator is arranged axially between thefirst and second bearings.

In some embodiments, the electric generator may include a generatorhousing having a shaft opening defined axially therethrough, thegenerator housing including a can receptacle and a cover attached to anend of the can receptacle, the generator housing defining an internalcavity for receiving the stator of the generator core.

In some embodiments, the rotor of the electric generator may be attachedto an inner shaft that is rotationally coupled to the fan shaft, and theelectric generator includes a bearing disposed between the generatorhousing and the inner shaft for supporting rotation of the inner shaftindependently from the fan shaft.

In some embodiments, the electric generator may comprise amotor-generator selectively operable in a first mode to generateelectrical power from driven rotation and in a second mode to driverotation low pressure drive shaft by receiving electrical power.

In some embodiments, the high pressure turbine spool may include anaccessory shaft coupled to the high pressure drive shaft to receivedriven rotation.

According to another aspect of the present disclosure, a turbofan gasturbine engine for propulsion of an aircraft may include a low pressurespool including a fan rotor arranged at a forward end of the engine, alow pressure turbine rotor arranged at an aft end of the engine, a lowpressure drive shaft extending along an axis and rotationally couplingthe fan rotor to receive driven rotation from the low pressure turbinerotor, a high pressure spool including a compressor rotor, a highpressure turbine rotor, and a high pressure drive shaft extending alongthe axis and rotationally coupling the compressor rotor to receivedriven rotation from the high pressure turbine rotor, and a low pressuregenerator including a generator core having a stator arranged about thelow pressure drive shaft and a generator rotor rotationally coupled tothe low pressure drive shaft.

In some embodiments, the low pressure drive shaft may include a fanshaft and a quill shaft having a base rotationally attached to the fanshaft and a flange extending radially from the base to rotationallyconnect the fan shaft to the low pressure generator.

In some embodiments, the base of the quill shaft may include a number ofsplines extending radially inward for connection with a number ofsplines of the fan shaft to rotationally couple the quill shaft and thefan shaft while permitting movement therebetween.

In some embodiments, the fan shaft may include a first bearing and asecond bearing arranged to support the fan shaft for rotational motionabout the axis, and the low pressure generator is arranged axiallybetween the first and second bearings.

In some embodiments, the low pressure generator may include a generatorhousing having a shaft opening defined axially therethrough, thegenerator housing including a can receptacle and a cover attached to anend of the can receptacle, the generator housing defining an internalcavity for receiving the stator of the generator core.

In some embodiments, the generator rotor may be mounted to an innershaft that is rotationally coupled to the fan shaft, and the lowpressure generator includes a first bearing disposed between thegenerator housing and the inner shaft for supporting rotation of theinner shaft independently from the fan shaft.

In some embodiments, the first bearing may contact the can receptacle,and the low pressure generator may include a second bearing disposedbetween the cover and the inner shaft for supporting rotation of theinner shaft independently from the fan shaft.

In some embodiments, the can receptacle may define a number oflubrication pathways extending radially therethrough for communicatingcooling oil to the stator of low pressure generator.

In some embodiments, the low pressure generator may include amotor-generator selectively operable in a first mode to generateelectrical power from driven rotation, and in a second mode to driverotation by receiving electrical power.

In some embodiments, the high pressure turbine spool may include anaccessory shaft coupled to the high pressure drive shaft to receivedriven rotation.

According to another aspect of the present disclosure, a turbofan gasturbine engine for propulsion of an aircraft may include a turbofanassembly for providing air to the engine, the turbofan assemblyincluding a fan shaft extending along an axis and adapted to receivedriven rotation about the axis from a low pressure turbine rotor of theengine and a fan rotor rotationally coupled to the fan shaft forrotation, a compressor assembly adapted to compress air received fromthe turbofan assembly, the compressor assembly including a compressorshaft extending along the axis and adapted to receive driven rotationabout the axis and a compressor rotor rotationally fixed to thecompressor shaft, and a low pressure generator including a statorarranged about the fan shaft and a rotor rotationally coupled to the fanshaft, the low pressure generator being positioned axially between thefan rotor and the compressor.

These and other features of the present disclosure will become moreapparent from the following description of the illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative embodiment of a turbofangas turbine engine with a portion cut away to show that the gas turbineengine includes a low pressure turbine spool and a high pressure spool,and showing that the low pressure spool includes a fan disposed on aforward end of the engine, a low pressure turbine rotor disposed on anaft end of the engine, and a low pressure drive shaft that extends alongan axis between the forward and aft ends and is connected to each of thefan rotor and the low pressure turbine rotor to transfer rotationaldrive from the lower pressure turbine rotor to the fan, and showing thatthe high pressure spool includes a compressor, a high pressure turbinerotor, and a high pressure drive shaft that extends concentrically withthe low pressure drive shaft and is connected to each of the highpressure turbine rotor and the compressor to transfer rotational drivefrom the high pressure turbine rotor to the compressor, and showing thatthe engine includes a low pressure electric motor-generator that ispositioned between the fan and the compressor along the axis and isrotationally coupled to the low pressure drive shaft for selectiveoperation as a generator to generate electric power from rotation of thelow pressure drive shaft or as an electric motor to assist rotation ofthe low pressure drive shaft;

FIG. 2 is a perspective view of a portion of the turbofan gas turbineengine of FIG. 1 in cross-section taken along the cross-sectional plane2-2 showing that the low pressure drive shaft includes a fan shaft and aquill shaft that is rotationally coupled to the fan shaft by a quillconnection that allows movement of the fan shaft relative to the quillshaft while transferring rotational drive, and showing that the lowpressure motor-generator includes a generator core having a rotorrotationally coupled with the quill shaft and a stator arranged outsideof the rotor and fixed against rotation relative to the rotor, andshowing that the low pressure motor-generator includes a generatorhousing positioned radially outside of the quill shaft and bearingsdisposed radially between the generator housing and the quill shaft, anda number of coolant pathways for distributing lubricant to the lowpressure motor-generator;

FIG. 3 is a perspective view of the low pressure motor-generator of FIG.2 showing that the generator housing includes a can receptacle and acover attached to the aft end of the can receptacle, and showing thatthe turbofan gas turbine engine includes an electrical assemblyconnected to the cover of generator housing and extending radiallyoutward from the low pressure motor-generator for connection with otherloads;

FIG. 4 is an exploded perspective view of the low pressure motorgenerator of FIGS. 2 and 3 showing that the generator housing includesan interior cavity for housing the low pressure motor-generator core anda shaft opening therethrough for receiving the low pressure drive shaft,and showing that the quill shaft includes splines extending inwardly toform the quill connection with the fan shaft;

FIG. 5 is a perspective view of a support frame of the turbofan gasturbine engine of FIG. 1 showing that the support frame includes anumber of struts extending radially to connect with a number of supportcollars of the support frame, and showing that the low pressuremotor-generator is positioned between the fan and the support framealong the axis;

FIG. 6 is a perspective cross-sectional view of the support frame ofFIG. 6 taken along the line 6-6 and showing that the electrical assemblyof the LP motor-generator includes a connector electrically connected tothe stator and attached to the housing of the low pressuremotor-generator, a terminal base attached to an outer collar of thesupport frame, and a number of busbars that extend between and connectto each of the connector and the terminal base, and showing that thebusbars extend radially through one of the struts to electricallyconnect the connector to the terminal base;

FIG. 7 is a partially diagrammatic view of the turbofan gas turbineengine of FIG. 1 showing that the engine includes a high pressuremotor-generator adapted to be driven for rotation by the high pressuredrive shaft, and showing that the engine includes a power control modulethat is electrically connected to each of the low pressuremotor-generator and the high pressure motor-generator and is arrangedfor selectively operating each of the low pressure and high pressuremotor-generators independently between the generation modes and thedrive modes, and showing that the power control module is connected tocommunicate electrical power with an optional energy storage device, andshowing by example that the power control module determines that steadystate operational conditions exist, and in response to steady stateconditions, the power control module operates the low pressuremotor-generator in the generation mode and distributes electrical powergenerated by the low pressure motor-generator to an electrical user andselectively exchanges electrical power with the energy storage device;

FIG. 8 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1 and 7 showing by example that the power control modulecan exchange power between low pressure motor-generator and highpressure motor-generator to adjust loads applied to low pressure andhigh pressure spools in order to improve engine efficiency;

FIG. 9 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1, 7, and 8 showing by example that the power controlmodule determines that high demand operational conditions exist and inresponse the power control module operates the low pressuremotor-generator in the generation mode and operates the high pressuremotor-generator in the drive mode to assist rotation of the highpressure drive shaft and reduce load on the high pressure spool, andshowing that the power control module selectively exchanges electricalpower with the energy storage device;

FIG. 10 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1 and 7-9 showing by example that the power controlmodule determines that in-flight restart operational conditions existand in, the power control module operates the low pressuremotor-generator in the generation mode and operates the high pressuremotor-generator in the drive mode to assist in-flight restart of theengine, and showing that the power control module receives electricalpower from the energy storage device;

FIG. 11 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1 and 7-10 showing by example that the power controlmodule determines that loss of engine power operational conditions existand in response, the power control module selectively operates the lowpressure motor-generator in the drive mode to provide thrust assist;

FIG. 12 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1 and 7-11 showing by example that the power controlmodule determines that hot engine off operational conditions exist inwhich the engine is desirably shut down but remains at relatively hightemperature and in response the power control module operates the lowpressure motor-generator in the drive mode to provide electricallydriven rotation of the fan to provide air to the engine for coolingengine components and expelling fumes;

FIG. 13 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1 and 7-12 showing that the power control module iselectrically connected to a second high pressure motor-generator of asecond gas turbine engine for individual selective operation betweengeneration and drive modes to permit selective distribution of powerbetween the engine and the second engine, and showing by example thatthe power control module determines that operational conditions do notmeet threshold efficiencies, and in response to determination thatoperational conditions do not meet a threshold efficiency of the lowpressure spool of the engine, the power control module receives electricpower from the second engine and operates the low pressuremotor-generator in the drive mode;

FIG. 14 is a partially diagrammatic view of the turbofan gas turbineengine of FIGS. 1 and 7-13 showing that the power control module iselectrically connected to ground power source and determines that coolengine off operational conditions exist in which the engine is desirablyshut down and remains at relatively cool temperature and in the powercontrol module operates the low pressure motor-generator in the drivemode to inhibit rotation of the fan rotor to prevent rotation of theengine; and

FIG. 15 is a perspective view of a cross-section of another illustrativeembodiment of the low pressure electric motor-generator of the turbofangas turbine engine of FIG. 1 taken along the plane 2-2 and showing thatthe low pressure drive shaft includes a fan shaft and a quill shaft thatis rotationally coupled to the fan shaft and extends from the fan shaftto rotationally connect the fan shaft and the rotor of the low pressuremotor-generator for rotation.

DETAILED DESCRIPTION OF THE DRAWINGS

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to a number of illustrativeembodiments illustrated in the drawings and specific language will beused to describe the same.

Gas turbine engines may be adapted for various uses, such as to propelaircraft, watercraft, and/or for power generation. The electrical powerdemands on gas turbine engines adapted for such uses are rapidlyincreasing due to the growing number and power requirement ofprocessors, actuators, and accessories. However, drawing additionalelectric power from high pressure (HP) driven electric generators canlimit the operation of the gas turbine engine, for example, bydecreasing certain operating margins at peak demand.

The present disclosure includes descriptions of gas turbine engines thatinclude low pressure (LP) motor-generators configured to supply ofelectric power. In certain adapted uses of the engines, for example,when adapted for use in an aircraft, the present disclosure includesdevices, systems, and methods for integration of low pressure (LP)motor-generators into turbofan gas turbine engines. Motor-generatorsinclude devices that can be selectively operated in a first mode togenerate electricity for use in other systems and in a second mode todrive mechanical rotation by consumption of electrical power.Coordinated operation of low pressure (LP) and/or high pressure (HP)motor-generators in response to various operational conditions promotesoperational flexibility and power management optimization.

As shown in FIG. 1, an illustrative turbofan gas turbine engine 10includes a fan 12, a compressor 14 having a compressor rotor 15, acombustor 16, and a turbine 18 having a high pressure (HP) turbine rotor20 and a low pressure (LP) turbine rotor 22, housed within a casing 24as shown in FIG. 1. The fan 12 draws air into the compressor 14 thatcompresses and delivers the air to the combustor 16. The combustor 16mixes fuel with the compressed air from the compressor 14 and combuststhe mixture. The hot, high-pressure exhaust products of the combustionreaction in the combustor 16 are directed into the turbine 18 to causerotation of the HP and LP turbine rotors 20, 22 about an axis 25 todrive the compressor 14 and the fan 12, respectively.

In the illustrative embodiment, the gas turbine engine 10 includes ahigh pressure (HP) spool 26 illustratively comprising the compressorrotor 15, the HP turbine rotor 20, and a high pressure (HP) drive shaft28 that extends along the axis 25 to couple the compressor 14 forrotation with the HP turbine rotor 20. In the illustrative embodiment,the gas turbine engine 10 includes a low pressure (LP) spool 30illustratively comprising the fan 12, the LP turbine rotor 22, and a lowpressure drive shaft 32 that extends along the axis 25 to couple the fan12 for rotation with the LP turbine rotor 22. In the illustrativeembodiment, the drive shafts 28, 32 are concentric shafts that extendalong the axis 25 between forward 34 and aft ends 36 of the engine 10.

In the illustrative embodiment as shown in FIG. 1, the engine 10includes a low pressure (LP) motor-generator 38 positioned between thefan 12 and the compressor 14 along the axis 25. As shown in FIG. 2, theLP motor-generator 38 illustratively includes a motor-generator core 40having a stator 42 fixed against rotation relative to the LP drive shaft32 and a rotor 44 coupled to the LP drive shaft 32 for rotation. Thestator 42 is illustratively includes a number of stator windings 43positioned radially outward of the rotor 44, such that each isillustratively arranged in electromagnetic communication. In someembodiments, the motor-generator core 40 may include any suitable typeand/or arrangement of electro-mechanical motor and/or generator. The LPmotor-generator 38 is illustratively adapted for selective operationbetween a generation mode to generate electrical power from rotation ofthe LP turbine 22 and in a drive mode to receive electrical power forapplying rotational force to the LP drive shaft 32.

As shown in FIG. 2, the LP drive shaft 32 illustratively includes a fanshaft 46 and a quill shaft 48 forming quill connections with each of thefan shaft 46 and a rotor hub 106 (on which the rotor 44 isillustratively mounted) to connect the rotor 44 for rotation with thefan shaft 46 while permitting relative movement therebetween. The quillshaft 48 illustratively includes a base 50 coupled to the fan shaft 46and a flange 52 extending from the base 50 for connection with the rotorhub 106. The rotor 44 of the LP motor generator 38 is illustrativelymounted on the rotor hub 106, which is supported by bearings 152, 154(as discussed below), while being connected for rotation with the LPdrive shaft 32 through the quill shaft 48. In some embodiments, a singlequill connection may be used to rotationally connect the LP drive shaft32 with the rotor 44 while permitting relative movement.

As best shown in FIGS. 3 and 6, the LP motor generator 38 illustrativelyincludes an electrical assembly 58 that electrically connects the LPmotor-generator 38 to electrical loads of the engine 10. The electricalassembly 58 illustratively includes a connector 62 attached to the LPmotor-generator 38, a set of three busbars 64 each having an end coupledwith the connector 62, and a terminal base 66 coupled to an opposite endof each of the busbars 64. As shown in FIG. 6, the busbars 64illustratively extend radially outward from the LP motor generator 38through a strut 56 of a support frame 54 of the engine 10 for connectionwith the terminal base 66 to communicate electric power to and from theLP motor-generator 38.

As shown in FIGS. 7-14, the turbofan gas turbine engine 10illustratively includes a high pressure (HP) motor-generator 68. The HPmotor-generator 68 is illustratively embodied as being coupled to anauxiliary shaft 69 to receive driven rotation from the HP drive shaft28. The HP motor-generator 68 is illustratively adapted for selectiveoperation in a generation mode to generate electrical power fromrotation of the HP turbine rotor 20 or in a drive mode to receiveelectrical power to assist rotation of the HP drive shaft 28.

In the illustrative embodiment, the turbofan gas turbine engine 10includes a power control module 70 for governing electric powerdistribution within the engine 10. The power control module 70 isillustratively electrically connected to each of the LP motor-generator38 and HP motor-generator 68. The power control module 70 is adapted toselectively receive and distribute electric power between the LP and HPmotor-generators 38, 68, electric power users 72 (such as an airframe ofa vehicle (aircraft) in adapted use of the engine 10), and an energystorage device 74 (such as a battery), according to operationalconditions of the engine 10 (and/or the vehicle).

As explained in detail below, the power control module 70 governselectric power management based on the operational conditions of theengine 10. Under some conditions, the power control module 70 can directelectric power to the HP motor-generator 68 to assist rotation of the HPdrive shaft 28 and/or reduce load on the HP turbine rotor 20. Under someconditions, the power control module 70 directs electric power to the LPmotor-generator 38 to assist rotation of the LP drive shaft 32 and/orreduce load on the LP turbine rotor 22. Under some conditions, the powercontrol module 70 communicates electrical power between one or both ofthe motor-generators 38, 68 and the energy storage device 74, and/orfrom any of the motor-generators 38, 68 and the energy storage device 74to electric power users 72. As shown in FIG. 13, the power controlmodule 70 can be electrically connected to a second engine 111 to governelectric power management between engines 10, 111.

Returning now to FIGS. 1 and 2, the fan 12 is illustratively disposed atthe forward end 34 of the engine 10. The fan 12 is illustrativelyattached to a fan shaft 46 of the LP drive shaft 32 for rotation aboutaxis 25. The fan 12 illustratively includes a fan rotor 76 and fanblades 78 that extend radially from the fan rotor 76. The fan rotor 76illustratively rotates the fan blades 78 about axis 25 to direct airaxially into the engine 10.

In the illustrative embodiment as shown in FIG. 2, the fan shaft 46 ofthe LP drive shaft 32 is embodied as a hollow shaft that extends throughthe LP motor-generator 38 for connection with the fan rotor 76. The fanshaft 46 is illustratively configured for splined connection with the LPdrive shaft 32, but in some embodiments may be integral with the LPdrive shaft 32. The fan shaft 46 of the LP drive shaft 32 receivesdriven rotation from the LP turbine rotor 22.

As shown in FIG. 2, the fan shaft 46 illustratively includes a firstsection 80 having an outer diameter, a tapered section 82 that extendsfrom the first section 80 along the direction of the axis 25 towards theforward end 34, and a hub 84 extending from the tapered section 82 alongthe axis 25 for connection with the fan 12.

In the illustrative embodiment, the first section 80 of the fan shaft 46is illustratively coupled with the LP turbine rotor 22 to receive drivenrotation. The first section 80 illustratively includes an outer surface86 having splines 88 that each extend along the direction of the axis 25and have a radial height for connection with the quill shaft 48 (alsoshown in FIG. 3). The outer surface 86 aftward of the splines 88illustratively contacts a shaft bearing 92 to provide rotational supportto the fan shaft 46.

As shown in FIG. 2, the first section 80 is illustratively positioned toextend axially though the LP motor-generator 38 to connect with thetapered section 82. The tapered section 82 illustratively includes atapered outer diameter that increases in size along the axial directionmoving towards the forward end 34. The tapered section 82 isillustratively positioned to extend axially through the LPmotor-generator 38 to connect with the hub 84.

As shown in FIG. 2, the hub 84 illustratively includes a tiered section90 adapted for contact with a shaft bearing 93 to support the LP driveshaft 32 for rotation within the engine 10. Each of the shaft bearings92, 93 are illustratively arranged to receive lubricant from a lubricantdistribution system 94 of the engine 10. The tiered section 90illustratively includes a constant outer diameter that contacts a shaftbearing 93 to reduce friction of the fan shaft 46 during rotation.

As shown in FIG. 2, the fan shaft 46 is coupled with the quill shaft 48for rotation. The quill shaft 48 is illustratively embodied as a hollowcoupler forming a quill connection with the fan shaft 46 and the rotorhub 106 on which the rotor 44 is mounted. The base 50 of the quill shaft48 illustratively includes a hollow cylinder 96 having an inner surface98 and splines 100 that each extend along the direction of the axis 25and have a radial height (also shown in FIG. 4). The splines 100 of thequill shaft 48 are illustratively arranged complimentary to the splines88 of the first section 80 of the fan shaft 46 to form the quillconnection to allow relative movement between the fan shaft 46 and thequill shaft 48 while providing rotational coupling therebetween. Thequill connection provides an offset from the fan shaft 46 to accommodatenon-concentric rotation of the fan shaft 46 during a fan imbalanceand/or blade off event, and/or axial misalignment therebetween.

The quill shaft 48 illustratively includes the flange 52 that extendsradially outward from the base 50 for rotational connection with the LPmotor-generator 38. The flange 52 illustratively includes a neck 102extending radially from the base 50 and a stem 104 connected to the neck102 and partitioned radially spaced apart from the base 50. The stem 104illustratively forms another quill connection to the rotor hub 106 ofthe LP motor generator 38 that supports the rotor 44 for rotation withthe LP drive shaft 32. The stem 104 illustratively includes splines 105formed on an outer surface thereof and complimentary to splines 107 formon an inner surface of the rotor hub 106 to form the quill connection toallow relative movement between the rotor hub 106 and the quill shaft 48while providing rotational coupling therebetween.

Referring to FIG. 3, the LP motor-generator 38 illustratively includes ahousing 108 having a receptacle 110 and a cover 112 attached to thereceptacle 110 and together defining an interior cavity 114 (as shown inFIG. 2) for receiving the motor-generator core 40. As best shown in FIG.2, the receptacle 110 illustratively includes an annular shell 116extending along the direction of the axis 25 between a forward end 118and an aft end 120, a mount flange 122 attached to the aft end 120 ofthe annular shell 116, and an overhang 124 attached to the forward end118 of the annular shell 116.

As best shown in FIG. 2, the overhang 124 includes a limb 126 thatextends radially inward from the forward end 118 of the annular shell116 and an extension 128 connected to a radially inward end 130 of thelimb 126. The extension 128 illustratively extends from the limb 126parallel to the axis 25 towards the aft end 120 spaced apart from theannular shell 116 by the radial length of the limb 126 to define aportion of the interior cavity 114. The mount flange 122 isillustratively embodied as an annular flange extending perpendicularlyto the axis 25 to receive connection of the cover 112.

The cover 112 illustratively includes a cover flange 132 for connectionto the mount flange 122 of the receptacle 110, an annular section 134extending from the cover flange 132 towards the aft end 36 of the engine10, and an overhang 136 extending from the annular section 134. In theillustrative embodiment, the annular section 134 has a tapered outerdiameter increasing in size move towards the forward end 34 along theaxis 25. The overhang 136 of the cover 112 illustratively includes alimb 138 extending radially inward from the aft end of the annularsection 134 and an extension 140 connected to the radially inward end142 of the limb 138. The extension 140 illustratively extends from thelimb 138 parallel to the axis 25 towards the cover flange 132 spacedapart from the annular section 134 to define a portion of the interiorcavity 114 of the housing 108.

In the illustrative embodiment as shown in FIG. 2, the extensions 128,140 are radially aligned and define a gap 142 axially therebetween. Whenthe motor-generator core 40 is received within the interior cavity 114,the rotor 44 is illustratively positioned within the gap 142 inelectromagnetic communication with the stator 42. The extensions 128,140 each respectively include an inner surface 144, 146 and an outersurface 148, 150 adapted to support a respective bearing 152, 154 of theLP motor-generator 38.

The bearings 152, 154 are each illustratively embodied as a roller ballbearing having an outer race 156 that contacts the inner surface 144,146 of the respective extension 128, 140 and an inner race 158 thatcontacts an outer surface 160 of the inner shaft 106 on which the rotor44 is mounted. In the illustrative embodiment, the rotor 44 is coupledto the inner shaft 106 at a position between the bearings 152, 154 forrotation with the fan shaft 46.

As shown in FIG. 2, the turbofan gas turbine engine 10 illustrativelyincludes the lubricant distribution system 94 embodied as lubricantconduits formed within portions of the casing 24 for communicatinglubricant, such as oil, to the bearings 92, 93, 152, 154 and the stator42. In the illustrative embodiment, the housing 108 of the LPmotor-generator 38 includes lubrication pathways 162 defined therein.The lubrication pathways 162 illustratively extend radially through theannular shell 116 to provide communication of lubricant from thelubricant distribution system 94 to the stator 42.

As shown in the illustrative embodiment of FIG. 3, the electricalassembly 58 is electrically connected to the LP motor-generator 38 toprovide three electrically isolated busses for 3-phase powercommunication. In some embodiments, the electrical assembly 58 may beconfigured to communicate any suitable number of phase power. Theconnector 62 of the electrical assembly 58 is illustratively attached tothe cover 112 at an aft side 164 of the LP motor-generator 38. Theconnector 62 includes a mount 166 connected to the cover 112 and a body168 that extends from the mount 166 to connect with the busbars 64.

In the illustrative embodiment, the mount 166 extends generally for alength between opposite ends 170, 172 thereof and includes a mount hole174 defined therethrough on each end 170, 172 to receive a fastener forconnection to the cover 112. The mount 166 is illustratively arrangedgenerally tangential to the annular section 134. The body 168illustratively extends from the mount 166 at a position between the ends170, 172 and in a direction perpendicular to the length of the mount166. The body 168 illustratively includes a side 176 facing radiallyoutward from the axis 25 having three recesses 176 defined therein forconnection with one of the busbars 64.

As best show in FIGS. 2 and 6, the connector 62 illustratively includesthree electrical connections 178 each comprising a socket 180 disposedwithin the body 168 and wires 182 connected to the socket 180. Eachsocket 180 is illustratively embodied as a receptacle formed ofconductive material and including interior threads 183 complimentary toexterior threads 184 of the busbars 64 to form a threaded connectionbetween the connector 62 and the busbars 64. In some embodiments, theconnector 62 may include a floating connection with the busbars 64 toallow thermal movement therebetween while maintaining electricalconnection.

In the illustrative embodiment as shown in FIG. 2, each of the wires 182is illustratively attached to one of the sockets 180 and is isolatedfrom the other wires 182. The wires 182 each illustratively extendthrough the body 168 and the mount 166 for connection with the stator 42of the LP motor-generator 38. The busbars 64 are illustrativelyelectrically connected to the LP motor-generator 38 via the electricalconnections 178.

Referring now to the illustrative embodiment as shown in FIGS. 5 and 6,the LP motor-generator 38 is positioned forward of the support frame 54of the engine 10 along the axis 25. The support frame 54 illustrativelyincludes a hub 186 surrounding the axis 25 for receiving the LPmotor-generator 38, a collar 188 arranged radially outward of the hub186, and the strut 56 extending radially between the hub 186 and thecollar 188.

As shown in FIG. 6, the hub 186 illustratively defines an interior space190 therethrough to receive the aft end of the LP motor-generator 38.The LP drive shaft 32 penetrates through the interior space 190 of thehub 186 for connection with the LP motor-generator 38. The strut 56illustratively connects with the hub 186 at an angular position of theconnector 62 relative to the axis 25 that is complimentary, andillustratively equal, to the angular position about the axis 25.

As best shown in FIG. 5, the strut 56 illustratively includes a smoothouter surface 192 to minimize flow resistance. The strut 56illustratively includes an interior cavity 194 defined therein thatextends radially between the hub 186 and the collar 188. The interiorcavity 194 illustratively receives the busbars 64 therethrough to extendbetween the connector 62 and the terminal base 66. Positioning thebusbars 64 within the strut 56 provides physical protection whilepermitting conductive cooling of the busbars 64 by air passed over thestrut 56.

In the illustrative embodiment, the busbars 64 are each embodied as arod formed of electrically conductive material, for example, copper. Thebusbars 64 each illustratively include the exterior threads 184 disposedon one end for fixed connection to one of the connector 62 and theterminal base 66, and a cylindrical shape on the opposite end toslidably connect with the other of the connector 62 and the terminalbase 66 to form a floating connection to accommodate thermal expansion.The busbars 64 are illustratively embodied to be secured within theinterior cavity 194 surrounded with potting compound 196 to electricallyisolate the busbars 64 from each other. The busbars 64 illustrativelyextend radially between the connector 62 and the terminal base 66 at anangle relative to a plane that is perpendicular to the axis 25.

As best shown in FIG. 6, the terminal base 66 is illustratively attachedto the collar 188 at a position spaced apart from the connector alongthe axis 25. The terminal base 66 illustratively includes a body 198having three slots 200 defined radially therethrough each including aterminal socket 202 arranged therein to slidably receive one of thebusbars 64 therein for electrical connection. The terminal sockets 202are each illustratively embodied to include a hollow cylinder section204 disposed within the body 198 and a stem 206 extending from thehollow cylinder section 204 radially outside of the body 198 as aterminal post for connection to electrical loads of the engine 10. Theterminal sockets 202 are illustratively formed of electricallyconductive material to communicate electric power between the LPmotor-generator 38 and electrical loads of the engine 10. In someembodiments, the busbars 64 may be fixedly connected to the terminalbase 66 and have a floating connection with the connector 62.

Referring now to the illustrative embodiments of FIGS. 7-14, the gasturbine engine 10 includes the power control module 70 that iselectrically connected to each of the LP motor-generator 38 and HPmotor-generator 68. As mentioned above, the power control module 70governs electric power management of the engine 10 based on theoperational conditions of the engine 10.

The power control module 70 is illustratively embodied as a main controlunit including a processor 208, a memory device 210 that storesinstructions for execution by the processor 208, communicationscircuitry 212 adapted to communicate signals with various components ofengine 10 as directed by the processor 208, and power distributioncircuitry 214 adapted to communicate electric power with any of themotor-generators 38, 68, power users 72, and the energy storage device74 as directed by the processor 208. The power control module 70determines operational conditions of the engine based on signalsreceived from various engine components and selectively operates the LPand HP motor-generators 38, 68 based on the determined operationalconditions.

In the illustrative embodiment as shown in FIG. 7, the power controlmodule 70 determines that the current operational conditions are steadystate conditions. The steady state conditions illustratively includeoperational conditions in which the loads on the HP spool and the LPspool are within normal operating ranges such that noelectrically-driven force of rotation on the drive shafts 28, 32 isprovided. Examples of such steady state conditions when the turbofan gasturbine engine 10 is adapted for use in an aircraft include ground idle,flight idle conditions, and/or flight cruise conditions.

In the illustrative embodiment, in response to steady state conditions,the power control module 70 is configured to operate the LPmotor-generator 38 in the generation mode. The power control module 70illustratively directs electric power generated by the LPmotor-generator 38 to the power users 72 and selectively communicateselectric power with the energy storage device 74. The power controlmodule 70 is illustratively embodied to selectively communicate electricpower with the energy storage device 74 based on the operationalconditions and the power storage levels of the energy storage device 74.

In the illustrative embodiment as shown in FIG. 8, the power controlmodule 70 determines that the current operational conditions include lowefficiency conditions. Low efficiency conditions include efficiencies ofeither of the HP spool 26 or LP spool 30 that are less than respectivepredetermined threshold efficiencies. In the illustrative embodiment,the efficiency of the HP spool 26 includes a fuel efficiency of the HPspool 26 as represented by an operating point of the compressor 14 alongan operating curve as reflected on a plot of pressure ratio versuscorrected flow.

In the illustrative embodiment, in response to determination of lowefficiency conditions, the power control module 70 can selectivelydirect electric power generated from the LP motor-generator 38 in thegenerator mode to the HP motor-generator 68 in the drive mode to adjustthe operating point of the compressor 14 along the operating curve toimprove fuel efficiency of the HP spool 26. In the illustrativeembodiment, the power control module 70 can selectively direct electricpower generated from the HP motor-generator 68 in the generator mode tothe LP motor-generator 38 in the drive mode to adjust the operatingpoint of the compressor 14 along the operating curve to improve fuelefficiency of the HP spool 26. Thus, the power control module canselectively adjust the operating point of the compressor 14 along theits operating curve to improve engine fuel efficiency. In someembodiments, such low efficiency conditions when the turbofan gasturbine engine 10 is adapted for use in an aircraft include conditionsin which any of the fuel efficiency and/or heat rate are less than apredetermined fuel efficiency and/or predetermined heat rate for eitherof the HP spool 26 or the LP spool 30.

In the illustrative embodiment as shown in FIG. 9, the power controlmodule 70 determines that the operational conditions include high demandoperational conditions. The high demand operational conditionsillustratively include low compressor surge margin conditions and/ordisruption of rotation of the fan 12. Low compressor surge marginillustratively includes the amount of operating margin between thecurrent compressor operating conditions and compressor surge conditionsbeing below a predetermined threshold value. Examples of such highdemand operational conditions when the turbofan gas turbine engine 10 isadapted for use in an aircraft include high altitude flight, fan 12disruption events (e.g., fan rotor and/or blade damage from ice, birds,debris, etc.).

In the illustrative embodiment, in response to high demand operationalconditions, the power control module 70 is configured to operate the LPmotor-generator 38 in the generation mode and to direct electric powerto the HP motor-generator 68 in the drive mode. For example, when thehigh demand operational conditions exist due to low compressor surgemargin, the power control module 70 illustratively reduces the load onthe HP Spool 26 by assisting rotation of the HP drive shaft 32 with theLP motor generator 38, and increasing the operating margin between thecurrent compressor operating conditions and compressor surge conditions.

In the illustrative embodiment as shown in FIG. 10, the power controlmodule 70 determines that the operational conditions include hotrestart. When the engine 10 is adapted for use in an aircraft, hotrestart operational conditions include in-flight restart conditions.Under such in-flight restart conditions, some ram air flow isillustratively received by the fan 12 because the aircraft is currentlyin flight. In response to hot restart operational conditions, the powercontrol module 70 is illustratively configured to operate the LPmotor-generator 38 in the generation mode and to direct electric powerto the HP motor-generator 68 in the drive mode to assist restart of theengine 10. The power control module 70 illustratively directs electricpower from the power storage device 74 to the HP motor-generator 68.

In the illustrative embodiment as shown in FIG. 11, the power controlmodule 70 determines that the operational conditions include loss ofengine power. Loss of engine power illustratively includes anoperational shut down of the engine 10, where operational shut downincludes elective shut down and unexpected shut down. In response todetermination of loss of engine power operational conditions, the powercontrol module 70 is configured to selectively operate the LPmotor-generator 38 in the drive mode to selectively rotate the LP spool30 to provide thrust assist. The power control module 70 illustrativelydirects electric power from the power storage device 74 to the LPmotor-generator 38. When the engine 10 is adapted for use in anaircraft, thrust assist can provide light and/or pulse thrust foradditional stability control, navigational control, range extension,and/or landing assist.

In the illustrative embodiment as shown in FIG. 12, the power controlmodule 70 determines that operational conditions include hot engine offconditions. Hot engine off conditions illustratively include engine 10being electively shut down while an operating temperature remains abovea threshold temperature. In the illustrative embodiment, the operatingtemperature includes a lubricant temperature. In response todetermination of hot engine off conditions, the power control module 70operates the LP motor-generator in the drive mode to drive air throughthe engine 10. Passing air through the engine 10 can cool enginecomponents and can provide pressure to prevent accumulation of exhaustproducts into certain areas.

In the illustrative embodiment as shown in FIG. 13, the power controlmodule 70 is electrically connected with other turbo fan gas turbineengines 111, illustratively three other engines 111. Engines 111 areillustratively embodied as similar to engine 10 and each of the engines10, 111 are illustratively adapted for use in the aircraft. In someembodiments, the engines 111 may be any type of engine adapted for usein the aircraft and capable of generating electric power. The powercontrol module 70 illustratively determines that electric high bypassconditions exist in engine 10. Electric high bypass conditionsillustratively include disengagement of engine 10 and one of the otherengines 111 but with electrically driven rotation of their fans 12 tomaintain high fan area.

In the illustrative embodiment, in response to determination of electrichigh bypass conditions, the power control module 70 operates the LPmotor-generator 38 of the engines 10, 111 in the drive mode toelectrically drive rotation of their respective fans 12. The powercontrol module 70 illustratively directs electric power from any of theoperating engines 111 and the energy storage device 74 to the disengagedengines 10, 111. Such selective electric high bypass operation promotesefficiency and flexibility across engines 10, 111 and their platforms.

In the illustrative embodiment as shown in FIG. 14, the power controlmodule 70 operates the LP motor-generator 38 to inhibit rotation of thefan 12 while the engine 10 is powered off. The power control module 70is illustratively connected to a stationary power source as indicated byground power 113. The power control module 70 illustratively directspower from the ground power 113 to the LP motor-generator 38 to inhibitrotation of the fan 12. Such operation can prevent accidental rotationof the engine 10 components from natural wind which can be damagingwithout operation of the engine 10.

In the illustrative embodiment, the power control module 70 determinesthe operational conditions based on signals received from various enginecomponents. The various engine components illustratively include atleast rotational speed sensors configured to detect the rotational speedof the LP and HP spools, compressor input and output pressure sensorsadapted to determine inlet and outlet pressures of the compressor 14. Insome embodiments, the various engine components may include any ofcompressor surge margin sensors adapted to detect the amount ofoperating margin between the current compressor operating pressure and acompressor surge pressure, fuel rate sensors, and/or efficiency sensors(including at least temperature and pressure sensors for determiningdifferentials across the LP turbine rotor 20 and HP turbine rotor 22)adapted to determine operating efficiency of the HP spool 26 and LPspool 30. In some embodiment, the engine 10 may include any numberand/or arrangement of sensors for detecting and/or determining currentoperational parameters. In some embodiment, the 3-phase powerarrangement may be used to determine LP shaft 32 speed indirectly.

In another illustrative embodiment as shown in FIG. 15, the gas turbineengine 10 includes low pressure (LP) motor-generator 1038 having amotor-generator core 1040 configured for selective operation between ageneration mode to generate electrical power from rotation of the LPturbine 22 and in a drive mode to receive electrical power for applyingrotational force to a LP drive shaft 1032. The LP motor-generator 1038is similar to the LP motor-generator 38 as disclosed herein.Accordingly, similar reference numbers in the 1000 series indicatefeatures that are common between the LP motor-generator 1038 and the LPmotor-generator 38 unless indicated otherwise. The description of the LPmotor-generator 38 is hereby incorporated by reference to apply to theLP motor-generator 1038 except in instances of conflict with thespecific disclosure of the LP motor-generator 1038.

The LP drive shaft 1032 illustratively includes a fan shaft 1046including a generator mount 1048 that extends radially from the fanshaft 1046 to support the motor-generator core 1040. In the illustrativeembodiment, the motor-generator mount 1048 is fixedly connected with thefan shaft 1046 both in rotation and radial movement. The motor-generatorcore 1040 illustratively includes a stator 1042 and a permanent magnetrotor 1044 that can operate in electromagnetic communication with thestator 1042 with radial spacing 1045 between the rotor 1044 and thestator 1042.

Unlike the LP motor-generator 38, the LP motor-generator 1038 does notinclude bearings 152, 154 independent from the shaft bearings 92, 93.Upon degradation and/or failure of any of the shaft bearings 92, 93 suchthat the fan shaft 1046 does not rotate concentrically with the axis 25such that the radial spacing 1045 is relatively large, the LPmotor-generator 1038 is adapted to continue to support operation despitethe increase in radial spacing 1045.

In some embodiments, the motor-generators disclosed herein may beconfigured for operation in only one of a power mode and/or a generatormode.

While the disclosure has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asexemplary and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of thedisclosure are desired to be protected.

What is claimed is:
 1. A turbofan gas turbine engine for use in anaircraft, the engine comprising a low pressure spool including a fanrotor arranged at a forward end of the engine, a low pressure turbinerotor arranged at an aft end of the engine, a low pressure drive shaftextending along an axis and rotationally coupling the fan rotor toreceive driven rotation from the low pressure turbine rotor, a highpressure spool including a compressor rotor, a high pressure turbinerotor, and a high pressure drive shaft extending along the axis androtationally coupling the compressor rotor to receive driven rotationfrom the high pressure turbine rotor, and an electric generatorpositioned axially between the fan rotor and the compressor rotor alongthe axis, the electric generator including a generator core having astator arranged about the low pressure drive shaft and a generator rotorrotationally coupled to the low pressure drive shaft radially inward ofthe stator, a generator housing that receives the stator of the electricgenerator, a forward bearing arranged forward of the stator that isengaged between the generator rotor and the generator housing, and anaft bearing arranged aft of the stator that is engaged between thegenerator rotor and the generator housing, wherein the low pressuredrive shaft includes a first shaft coupled for rotation with the fanrotor and a second shaft that extends from the first shaft to thegenerator rotor of the electric generator, the second shaft includes anumber of radially-outwardly extending splines that engage with a numberof splines of the generator rotor to couple the generator rotor to thesecond shaft for rotation therewith, and the second shaft has a flangewith a frustoconical shape extending radially outward and axiallybetween the first shaft and the electric generator.
 2. The engine ofclaim 1, wherein the second shaft includes a number of splines extendingradially inward that engage with a number of splines of the first shaftto rotationally couple the second shaft and the first shaft.
 3. Theengine of claim 1, wherein the first shaft includes a first bearing anda second bearing each arranged to support the first shaft for rotationabout the axis, and the electric generator is arranged axially betweenthe first bearing and the second bearing.
 4. The engine of claim 1,wherein the generator housing has a shaft opening defined axiallytherethrough, the generator housing includes a can receptacle and acover attached to an end of the can receptacle, and the generatorhousing defines an internal cavity for receiving the stator of thegenerator core.
 5. The engine of claim 1, wherein the electric generatorcomprises a motor-generator selectively operable in a first mode togenerate electrical power from driven rotation and in a second mode todrive rotation of the low pressure drive shaft by receiving electricalpower.
 6. The engine of claim 1, wherein the high pressure turbine spoolincludes an auxiliary shaft coupled to the high pressure drive shaft toreceive driven rotation.
 7. A gas turbine engine for use in an aircraft,the engine comprising a low pressure spool including an output rotorwith blades arranged at a forward end of the engine configured toaccelerate air upon rotation of the blades, a low pressure turbine rotorarranged at an aft end of the engine, a low pressure drive shaftextending along an axis and rotationally coupling the output rotor toreceive driven rotation from the low pressure turbine rotor, a highpressure spool including a compressor rotor, a high pressure turbinerotor, and a high pressure drive shaft extending along the axis androtationally coupling the compressor rotor to receive driven rotationfrom the high pressure turbine rotor, and a low pressure generatorpositioned axially forward of the compressor rotor along the axis, thelow pressure generator including a generator core having a statorarranged about the low pressure drive shaft and a generator rotorrotationally coupled to the low pressure drive shaft radially inward ofthe stator, a generator housing that receives the stator of the lowpressure generator, a forward bearing arranged forward of the statorthat is engaged between the generator rotor and the generator housing,and an aft bearing arranged aft of the stator that is engaged betweenthe generator rotor and the generator housing, wherein the low pressuredrive shaft includes a first shaft coupled for rotation with the outputrotor and a second shaft that extends from the first shaft to thegenerator rotor of the low pressure generator, the second shaft has anumber of extending splines that engage with a number of splinesincluded in one of the generator rotor and the first shaft, and thesecond shaft has a flange with a frustoconical shape extending radiallyoutward and axially between the first shaft and the low pressuregenerator.
 8. The engine of claim 7, wherein the second shaft includes anumber of radially-outwardly extending splines that engage with a numberof splines of the generator rotor to couple the generator rotor to thesecond shaft for rotation therewith.
 9. The engine of claim 7, whereinthe second shaft includes a number of splines extending radially inwardthat engage with a number of splines of the first shaft to rotationallycouple the second shaft and the first shaft.
 10. The engine of claim 7,wherein the first shaft includes a first bearing and a second bearingeach arranged to support the first shaft for rotation about the axis,and the low pressure generator is arranged axially between the firstbearing and the second bearing.
 11. The engine of claim 7, wherein thegenerator housing has a shaft opening defined axially therethrough, thegenerator housing includes a can receptacle and a cover attached to anend of the can receptacle, and the generator housing defines an internalcavity for receiving the stator of the generator core.
 12. The engine ofclaim 7, wherein the low pressure generator comprises a motor-generatorselectively operable in a first mode to generate electrical power fromdriven rotation and in a second mode to drive rotation of the lowpressure drive shaft by receiving electrical power.
 13. The engine ofclaim 7, wherein the high pressure turbine spool includes an auxiliaryshaft coupled to the high pressure drive shaft to receive drivenrotation.
 14. An aircraft comprising an airframe, and a gas turbineengine including: a low pressure spool including an output rotor withblades arranged at a forward end of the engine configured to accelerateair upon rotation of the blades, a low pressure turbine rotor arrangedat an aft end of the engine, a low pressure drive shaft extending alongan axis and rotationally coupling the output rotor to receive drivenrotation from the low pressure turbine rotor, a high pressure spoolincluding a compressor rotor, a high pressure turbine rotor, and a highpressure drive shaft extending along the axis and rotationally couplingthe compressor rotor to receive driven rotation from the high pressureturbine rotor, and a low pressure generator positioned axially forwardof the compressor rotor along the axis, the low pressure generatorincluding a generator core having a stator arranged about the lowpressure drive shaft and a generator rotor rotationally coupled to thelow pressure drive shaft radially inward of the stator, a generatorhousing that receives the stator of the low pressure generator, aforward bearing arranged forward of the stator that is engaged betweenthe generator rotor and the generator housing, and an aft bearingarranged aft of the stator that is engaged between the generator rotorand the generator housing, wherein the low pressure drive shaft includesa first shaft coupled for rotation with the output rotor and a secondshaft that extends from the first shaft to the generator rotor of thelow pressure generator, the second shaft has a number of extendingsplines that engage with a number of splines included in one of thegenerator rotor and the first shaft, and the second shaft has a flangewith a frustoconical shape extending radially outward and axiallybetween the first shaft and the low pressure generator.
 15. The aircraftof claim 14, wherein the second shaft includes a number ofradially-outwardly extending splines that engage with a number ofsplines of the generator rotor to couple the generator rotor to thesecond shaft for rotation therewith.
 16. The aircraft of claim 14,wherein the second shaft includes a number of splines extending radiallyinward that engage with a number of splines of the first shaft torotationally couple the second shaft and the first shaft.
 17. Theaircraft of claim 14, wherein the low pressure generator comprises amotor-generator selectively operable in a first mode to generateelectrical power from driven rotation and in a second mode to driverotation of the low pressure drive shaft by receiving electrical power.18. The aircraft of claim 14, wherein the gas turbine engine includes ahigh pressure motor-generator coupled to the high pressure spool to bedriven by the high pressure drive shaft.
 19. The aircraft of claim 18,wherein the output rotor is provided by a turbofan.